My heater fan in 1998 Ford Windstar only has high speed the other three speeds do not work have taken the speed selecter switch apart and it looks very simple a raised metal ball makes contact with metal plates can not understnd why it isnt working. When I cross the bare wires the fan will operate in different speeds

Normally when lower speeds stop working it is due to the resistor pack. Resistors are added to the circuits to decrease the blower speed. This may not apply in your instance since you can short out the contact to get the lower speeds to operate. Are you certain the fan is actually operating at lower speeds? or is it the same speed when you short out the contacts?